1. Field of the Invention
This invention relates to a method and apparatus for monitoring the position of a sheet strip material passed through a stamping device, and more particularly, to a method and apparatus for detecting a sheet strip material misfeed condition within the stamping device as the sheet strip material progresses through the stamping device. This invention also discloses a method and apparatus for detecting the configuration of individual connected stamped items in a strip produced by a stamping device to detect individual stampings having a configuration deviating from a desired stamping configuration.
2. Description of the Prior Art
It is well known in the stamping art to pass a sheet strip material through a stamping device to produce a plurality of individual frames or stampings in the sheet strip material. The individual frames or stampings each have a configuration dependent upon the placement of the various punches in the movable portion of the stamping device. As the sheet strip material is passed through the stamping device, the movable portion of the stamping device is cycled into and out of contact with the sheet strip material to blank stock from the sheet strip material to provide a plurality of individual frames or stampings. After the individual frames exit the stamping device, the individual frames may be separated from one another for further use.
Since the stamping device operates at a high rate of speed, a sheet strip material misfeed condition within the stamping device or other problem that may develop within the stamping device resulting in frames being produced having an undesired configuration are normally undetected unless the stamping device operator shuts the system down and performs a visual inspection of the individual frames or stampings. Generally, by the time the operator stops the stamping device to inspect the individual frames or stampings, the misfeed condition or other problem has resulted in a large number of frames or stampings being produced having an undesirable configuration. These frames or stampings must be removed from the sheet strip material for scrap.
As known in the art, a sheet strip material misfeed condition is identified as any condition, occuring either internally or externally to the stamping device, which prevents the sheet strip material from being at its proper location within the stamping device at any preselected instant of time relative to the movable portion of the stamping device.
In order to provide an early indication of a sheet strip material misfeed condition within the stamping device, various devices have been utilized.
Spring loaded micro-switches or other suitable contact-type switches have been employed internal to the stamping device to provide a material misfeed indication to the stamping device operator if the sheet strip material passing through the stamping device rolls over on itself or buckles within the stamping device. When this roll-over or buckle condition occurs, up to three layers of sheet strip material are provided to the movable punch assembly portion of the stamping device. When this occurs, the movable punch assembly is inhibited in its length of travel and, as a result, the micro-switch is not closed. If the micro-switch fails to close, a signal is provided to notify the stamping device operator of the roll-over or buckle condition. The use of a micro-switch or other mechanical switch internal to the stamping device is undesirable since the micro-switch can only detect a roll-over or buckle condition if the movable portion of the stamping device is inhibited in its full length of travel. In addition, the micro-switch will detect a roll-over or buckle condition only after the roll-over or buckling has occurred. The micro-switch cannot detect other types of misfeed conditions such as a change in the speed of the sheet strip material passing through the stamping device or a momentary jamming of the sheet strip material within the stamping device. In addition, the micro-switch cannot detect other conditions or problems which occur internal to the stamping device which result in individual frames or stampings being produced having a configuration other than the desired configuration.
Therefore, there is a need for a non-contact detection apparatus for use with a stamping device that is capable of detecting a sheet strip material misfeed condition and also capable of detecting a deviation in the configuration of an individual frame or stamping from the desired frame configuration.
Although non-contact detecting devices are commercially available, these non-contact detecting devices are limited in that they only detect the thickness of a sheet strip material, or the presence or absence of a sheet strip material at a preselected location.
U.S. Pat. No. 2,587,631 discloses a method and device adapted to detect magnetic sheets which vary from a predetermined standard of thickness. U.S. Pat. No. 2,700,132 discloses a device for preventing the feeding of more than one thickness of magnetic sheet material into printing, fabricating or other sheet or blank treating machines, and includes an electronic double detector having an electromagnetic detecting head which is disposed in the path of travel of the sheets or blanks.
U.S. Pat. Nos. 2,994,015 and 3,069,601 disclose a magnetic detector for gauging or measuring the thickness of ferro-magnetic sheet material passed in proximity to a pair of magnetic detector heads.
U.S. Pat. No. 4,019,131 discloses a method and apparatus for measuring the shape of the wavy edges of metal strips. The measuring apparatus comprises an electromagnetic induction type non-contacting distance measuring device including a detection coil disposed near the edge of a running metal strip, a filter for deriving out the high frequency component and the low frequency component of the output of the detection coil, and means responsive to the high frequency component for determining the contour of the wavy edge of the strip. The device also includes a means responsive to the low frequency component for adjusting the lateral position of the detection coil with respect to the wavy edge of the metal strip.
U.S. Pat. No. 4,134,486 discloses a workpiece detection circuit in an article handling apparatus for aborting a workpiece from the apparatus whenever an unanticipated workpiece presence or absence is sensed.
U.S. Pat. No. 4,138,709 discloses a proximity switch which is adapted to close a circuit between a source and a load when a metal object is adjacent to the coil in the switch.
U.S. Pat. No. 4,420,747 discloses a sheet feed monitoring system for detecting missing or superimposed sheets fed to a sheet processing machine. The system includes a measuring device for generating signals increasing with the number of superimposed sheets and an evaluating device for emitting an electrical signal when irregularities occur.
While it has been suggested by the prior art devices to utilize contact-type switches to detect a sheet strip material roll-over or buckle condition within the stamping device and to utilize non-contact sensing devices to determine the thickness or presence of a sheet strip material at a preselected location, there is a need for an improved method and apparatus for detecting a sheet strip material misfeed condition within a stamping device as the sheet strip material progresses through the stamping device. The misfeed detection apparatus must be capable of generating a waveform which identifies each individual frame, stamping or stamped item passed through the stamping device. Each waveform identifies an individual frame or stamping as a function of the position of the movable portion of the stamping device. The apparatus must also include means for comparing the plurality of waveforms generated to detect a deviation between waveforms. The deviation between waveforms identifies a material misfeed condition within the stamping device.
In addition to producing an individual waveform for each frame or stamping to detect the presence of a sheet strip material misfeed condition, the apparatus must be capable of being used as a means for detecting the configuration of the individual frames or stampings produced by the stamping device even when no material misfeed condition exists. When used as a frame configuration apparatus, the apparatus generates an individual waveform which identifies the configuration of each frame or stamping produced by the stamping device as a function of the movable portion of the stamping device. The apparatus includes means for selecting a desired waveform identifying a desired frame configuration as a reference waveform. The reference waveform identifying the desired frame configuration is compared to following waveforms to detect a deviation or change in the configuration of at least one individual frame from the desired frame configuration.
When either a material misfeed condition or a frame configuration deviation is detected, the apparatus must be capable of providing a signal to the stamping device to initiate stoppage of the stamping device to allow the material misfeed condition to be corrected or to limit production of individual frames having a configuration deviating from the desired frame configuration.